Strip metal rolling process and apparatus



Oct. 6, 1953 MlCHEL STRIP METAL ROLLING PROCESS AND APPARATUS INVENTOR f/dI/Iids Niche! ATTORNEY Patented Oct. 6, 1953 STRIP METAL ROLLING PROCESS AND APPARATUS Mathias Michel, Pittsburgh, Pa., asslgnor to Aluminum Company of America, Pittsburgh, Pin, a corporation of Pennsylvania Application February 16, 1949, Serial No. 76,761

5 Claims.

The present invention relates to cold rolling of strip metal stock in the production of cold rolled strip or sheet metal and it has to do particularly with reduction and temper or finish rolling of coiled strip or sheet metal wherein the entire length of each coil is rolled under tension in a cold rolling strip mill.

Large tonnages of cold rolled strip metal or sheet in various widths and thicknesses and in many kinds of metals and alloys are currently being produced in high speed strip mills by a method which involves for one rolling operation initially unwinding strip from a coil on a reel, entering the unwound end of the strip between the working rolls of a mill, passing the entire length of the strip through the mill, subjecting the strip to front and back tension, the value of which is substantially greater than that needed merely to render the stri taut, and recoiling the rolled strip emergin from the mill into tight mill coils for further handling and processing. A multiplicity of such rolling operations are required to reduce the strip from a heavy starting gauge or thickness to a desired finish gauge, the number depending on the gauge desired, and to produce the temper, finish, flatness and other characteristics desired of the strip product in the mill coils.

conventionally, in this rolling method, the practice is to decelerate the mill from its normal rolling or delivery speed to a slow threading speed of but a few hundred feet per minute, roll speed, each time the strip end from a new coil is to be entered for rolling and to run the mill at threading speed until sufiicient length of strip passes through the mill to enable several wraps thereof to be formed on a recoiling or delivery reel behind the mill. This low threading speed is required in order to avoid rupture of the strip by the sudden shock loading or pull imposed thereon in eflecting acceleration of the strip coil when the rolls grip the presented end of the strip and start it feeding or traveling at roll speed. The lighter the gauge of the strip presented to the mill rolls and the larger and wider the coil, some weighing several tons and more, the lower the threading speed of the mill has to be to bring the starting stress on the strip down to a point which it can withstand.

Moreover, it is desirable to employ an electric unwind for the strip coil for various well known reasons. Such an unwind, embodying expansible cones or a reel with which to axially support and grip the coil and a drag generator to back tension the strip, is well known. The strip, upon entry,

not only has to accelerate the coil, but the unwind and associated drag generator. The starting inertia or WR. which the strip is required to overcome, as heretofore entered into the mill, is thus greatly increased, particularly since speed change earing usually is required between the reel and generator thereby necessitating a low mill threading speed to avoid strip rupture.

After the initial feeding and threading operations have been eiiected, the practice has been to accelerate the mill to a given rolling speed, such speed varying with different mills and materials. Ordinarily, for a mill of moderately high speed, it is at least several times greater than threading speed and in some instances as much greater as ten times threading speed. Hereinafter, rolling speed means that speed of the rolls at which a given strip mill is customarily operated after acceleration in rolling a given material.

A serious objection to this prior method is that since the conditions with respect to speed and tension are not stabilized until the rolling speed is reached, most of that portion of the strip which has passed between the mill rolls prior to stabilization is off gauge and eventually must be out off and discarded as scrap. In the operation of a moderately high speed strip mill, it is not unusual to have 50 to '75 feet of oil gauge strip produced on every coil due to changing mill speed from threading speed to rolling speed which in the tonnages involved amounts to a serious scrap loss, reduces efficiency and total output and increases costs materially. The low speed threading operation increases non-production mill time. Further, the highest desirable rolling speed for a given mill may be limited by the economics of off gauge material resulting from the current practice of initially accelerating to rolling speed and while slowing at the end of every coil.

It is a primary object of the present invention to provide an improved method generally of the above described character in which the mill is continuously operated at rolling speed and accelerating torque is applied to an axially supported coil of strip tQ %99 el7ainit-for pay off and feed ofits leading end towards the mill to a feed rate substantially equal to the entry speed of the mill at the moment of entry of the end of the strip between the mill rolls.

Another object of the invention is to provide a method of entering and rolling coiled strip as aforesaid wherein the strip in and unwound from the coil is relieved .of excessive coil starting inertia incident to seizure of the entering end of the strip by the mill rolls operating at rolling speed 3 and further wherein the strip is back tensioned immediately upon such entry.

A further object is the provision of an improved method and apparatus for the purpose indicated above which is operative to effect flying entry of coiled strip into a rolling mill operating at preset rolling rate with approximate matching of the strip and rolling speeds at entry and immediately upon entry to effect back tensioning of the strip so that practically the entire length of the coiled strip will be subjected to back tension rolling in the mill under substantially uniform and continuous speed and tension conditions whereby the productive efficiency of the mill and total usable output of the mill product are substantially increased at an overall reduction in production costs.

Still another object is to provide coiled strlp entry and tensioning apparatus and improved control means therefor which shall be simple in construction, reliable in operation and further characterized by sensitivity and automatism.

It is another object of the invention to provide a coiled strip decoiling system which prevents any jerky or uneven feed of the materia1 and keeps it continuously taut as it is withdrawn from the coil and which accelerates the coil and the withdrawn strip to a feed rate approximating that of continuously operating high speed strip processing apparatus which is to receive and operate upon it.

These and other objects, advantages and details of the invention will hereinafter appear in the specification and claims.

For the purpose of making the invention quite clear, reference is made to the accompanying drawing forming a part of this specification, wherein:

Fig. 1 is a diagrammatic representation of pre-' ferred apparatus for carrying out the invention, some parts being shown in elevation, some in section and others schematically;

Fig. 2 is an elevational view partly in section showing on an enlarged scale a portion of the apparatus of Fig. 1;

Fig. 3 is a view of the right side of the mechanism of Fig. 2 looking from the front thereof, the left side being a substantial duplicate, and

Fig. 4 is a simplified wiring diagram of the automatic acceleration and tension control mechanism.

In carrying out the invention, various well known types of cold strip mills and auxiliaries may be used, particularly those commonly employed in the production of wide and thin varieties of strip at high rolling speeds. As an example, aluminum strip is commonly made in widths up to '72 inches and of a thickness of .006 inch and heavier. Coil sizes may range from about 700 pounds to about 6,000 pounds and typical rolling speeds may be of the order of about 600 to 1,500 feet per minute. For other kinds of metals and alloys, and with various strip mills presently in use, coil weights and rolling speeds will vary from those mentioned.

As illustrated in Fig. 1, the preferred strip mill apparatus of the invention comprises a two high mill 1, a coil gripping pay off reel or unwind 8 disposed forwardly of the entering side of the mill, a feed roll and bridle mechanism 9 intermediate the reel and the mill and preferably disposed between the housings of the mill, a takeup or delivery reel Ill at the exit side of the mill, and a belt wrapper ll translatable toward and away from reel l0 by suitable means such as power cylinder l2. In its advanced position, the belt wrapper cooperates with reel [0, driven by electric motor 13 in usual relation to mill speed to exert forward pull on the strip, to direct the end of strip emerging from the mill around the reel so that the initial turns of a coil will be formed on the reel, after which the belt wrapper is retracted. Heretofore, it has been customary to effect this initial recoiling operation at mill threading speed, thereby delaying reaching rolling speed; but, by this invention, such delay is eliminated and the strip is caught on the fly at rolling speed. To assure proper reception of the end of the strip at the reel, strip guides [4 extending from the mill towards the reelare provided and such guides are supplemented by means of an inclined guide [5 on the belt wrapper, which guide closes any gap between the guides l4 and the belt roller IS in the advanced position of the belt wrapper, as shown in dotted lines, so that the strip end is directed onto the moving belt I1 and passed thereby around the reel [0.

The mih i is provided with a pair of working rolls [I87 of any suitable diameter journaled in usual "fashion in housings l5 and adapted for vertical adjustment by suitable roll adjusting mechanism (not shown) so as to provide the desired pass gap therebetween. The rolls are driven in unison in any conventional manner, such as by an electric motor 20 operating through reduction gear 2 I, the driving power being transmitted to both rolls by means of the usual drive spindles and pinions (not shown). For a purpose hereinafter described, a D. C. series motor 22 is suitably coupled to the main motor 20 as by means of the V-belts and pulleys shown and a D. C. exciter 23 is coupled to motor 22 and are consequently operated at a speed proportional to mill speed. The torque of motor 22 is additive to that of motor 20.

Instead of the two high mill 1, a four high mill, or a cluster mill, may be used, and where used as the last or finishing pass or for tempering, the work rolls thereof should be of a relatively large diameter, of the order of about 16 inches or up, to eifectively flatten and impart a smooth finish to the strip. A tandem mill may be used, if desired.

Pay off reel or mandrel 8 is of the expansiblecontractible type adapted for the axial charging of a strip coil 24 thereon from which strip S is fed to the mill. The reel is coupled through suitable reduction gear 29 to a dynamo-electric machine 25 (hereinafter termed machine) operated during initial feed of the strip to the mill as a motor and after entry of the strip into the mill as a drag generator to impose a predetermined back tension on the strip. While its output may be suitably dissipated, it preferably is fed back into th mill through the auxiliary motor 22. Suitable mechanism for handling and charging the strip coils onto the reel includes a reciprocating carriage or buggy 26 movable, as by means of power cylinder 21, axially of the reel 8 and provided with vertically adjustable roller cradle 28. The buggy with a strip coil 24 supported on its cradle 28 in axial alignment with the reel in its collapsed condition, is moved under the reel to thread the coil onto the reel into a central position in alignment with the longitudinal center line of the mill. Thereafter, the reel is expanded into tight gripping engagement with the inner wrap of the coil, the cradle lowered and the buggy moved out from under the coil, the grip of the reel on the coil preventing relative rotation therebtween and being effective for transmitting the full power of machine as a motor to cause rotation of the coil without slippage and being equally efiective when rotation of the coil is being retarded for back tensioning of the strip.

Instead of the reel type of coil pay off, the use of expansible cone type unwind, such as is disclosed in Mikaelson patent, No. 2,177,577, dated October 24, 1939, is contemplated, in which case the coils may be delivered to the unwind by suitable means well known in the art.

The end of strip S unwound from coil 24 is passed over a billy roll and between top and bottom guides 3| and inserted between a pair of open pinch feed rolls J1 andjg of the feed and bridlm, the framework of which includes side plates 34 detachably connected to the mill housings l9 and mounted on wheels 35 to facilitate removal of this mechanism when necessary, as for mill roll changing. Bottom feed roll 33 is journaled at its ends in side plates 34 with its top on a level with that of the bottom mill roll I8. Top feed roll 32 is supported at its ends in suitable bearings carried by slide blocks 36 slidable vertically in guide ways 31 on the outer sides of the side plates 34. Each slide block 36 is pivotally connected at 38 to the upper end of a lifting rod 40, the lower portion of which is of reduced diameter and extends through a central bore in a cylindrical bearing 4| turnably mounted in the bifurcated end of arm 42 fastened on cross shaft 43. Each bearing 4| is provided with flats at the ends of the rod bore therethrough, the shoulder formed by the reduced diameter portion of the rod seating on the upper flat and. a spring bearing 44 being held against the lower flat by a compression spring 45 on the rod, which spring, by adjustment of its retaining nut 46 threaded on the rod, is adapted to regulate the pressure of the top feed roll 32 upon the strip S when the feed rolls are closed. Centrally along shaft 43 an arm 41 is secured and an operating rod 48 is pivoted at 49 thereto, the rod 48 being an extension of a piston rod secured to a piston (not shown) operating in a cylinder 50 which is trunnion supported on suitable brackets secured to the base of the framework. Normally, pressure is admitted to cylinder 50 so as to cause the top feed roll 32 to be held in raised position relatively to fixed roll 33 and thus provide an open pass for free entry of the strip. After strip entry, the fluid pressure is admitted to the opposite end of cylinder 50 to effect movement of the feed roll 32, through the operating connections described, down into pinching engagement with the strip S. Lower roll 33 is not driven but may be, if desired. The upper roll 32 is driven from electric motor 5| through a suitable spindl coupling (not shown).

At the entry side of the feed rolls, means is provided to effect centering of the free end of strip S with respect to coil 24 and mill 1 in case it is askew. Suitably, such means comprises laterally movable side guides in the form of vertically disposed rollers 52 carried by bars 53. Each bar has a rib 54 passing up through an elongated slot in a transversely disposed trough member 55 secured at its ends to a U-bracket56 carried by the side plates 34. In the trough of member 55, two opposed L-shaped slides 51 are disposed, one for each side guide and to the short leg of which the rib 54 of the guide is suitably secured. The long leg of each slide is provided with rack bar teeth in mesh with a pinion 58 disposed between the legs, which pinion is journaled in member 55 midway of its length. By means of a cylinder 59 secured to the left side of bracket 56, whose piston is connected to rod 60 having screw threaded connection with nut 5| secured to one of the slides 51, both slides are actuated to move the side guides 52 in and out. Reduced end portion of rod 60 slidably passes through an upstanding lug on the end of trough member 55 remote from cylinder 59 and its squared end 62 is adapted to receive wrench or tool, by which the rod 60 may be turned to adjust the position of the guides 52. This adjustment is made initially for the width of strip being operated upon to the point where the rollers 52 in their in position will lightly bear against the edges of the strip S when it is laterally centered.

It may be here stated that after the end of a strip S has been entered between the open feed rolls, pressure fluid is admitted into cylinders 59 and 50 sequentially in order first to actuate the side guides to in position and thereby center the strip, if 01? center, and then to close the said rolls on the centered strip for power feeding to the mill.

The strip end leaving the feed rolls travels through a vertically narrow tunnel or passageway defined by upper and lower guide members 64 of any suitable form and appropriately secured to the side plates 34, whereby the strip is guided into the pass between the mill rolls 18. A group of bridling rollers 65 is preferably included in the tunnel for use as a hold-back for the trailing end of strip passing to the mill, the upper rollers of the group being vertically movable and in their lower position being disposed between adjacent pairs of the fixed lower rollers whereby the strip is caused to take a sinuous path as it is drawn toward the mill rolls. As here shown. the lower bridle rollers are journaled in the side plates 34, while the upper rollers are journaled in vertical slides 66 guided by usual rails, or otherwise, and adapted to be raised and lowered by power means such as cylinder 81 mounted on a cross frame at the top of side plates 34, its piston 68 being suitably connected to a cross head 69 to the ends of which the slides 66 are connected. The extent of intermeshing of the bridling rollers and consequently the degree of strip bending and resultant hold-back tensionmg may be controlled by any suitable adjusting means limiting the downstroke of piston 68. The bridle rollers are open during feed entry of the strip into the mill. Additional offset rollers adapted by adjustment to control the angle of entry of strip passing through the mill are shown for use in production of bright finish strip, but they are unnecessary to the instant invention and may be omitted, if desired.

The method of operation of the described strip mill embodies three fundamental steps difl'erentlating it from prior practice: (1) operating the mill continuously at rolling speed, (2) effecting strip coil acceleration and flying entry of the strip into the mill at a speed proportioned to the mill roll speed, and (3) immediately upon entry, back tensioning the strip, whereby substantially the steady state conditions as to roll ng speed and back tension are realized and rollmg of ofi gauge material practically eliminated. Of course, it will be appreciated that, as heretofore intimated, the mill rolling speeds, the strip thicknesses and the material of which it is composed will vary quite widely thereby affecting the percentage differential between strip speed and roll speed which may exist at entry without causing strip rupture. Hence, exact matching of strip and roll speeds is not required; since, obviously, the strip will sustain a pull below its rupture strength. Acceleration of the coil and strip to a feed rate or entry speed of between about 70 per cent to 110 per cent of roll speed may be effected and a feed rate of about 80 per cent of roll speed for material of .040" thickness and lighter is preferred and has been found practical and satisfactory in use.

Means are provided to control the acceleration, effect switch-over automatically to back tension upon strip entry and to control the tension during rolling. With reference to Fig. 4, mill motor 20 has its armature and shunt field connected to D. C. supply source through controller II embodying usual starting and speed adjusting controls which are operated to start the mill motor and cause it to drive the mill at desired rolling speed. Feed back motor 22 and machine 25 have their armatures l2 and 13, respectively, connected in loop circuit by conductors l4 and 15. Armature current is adapted to be supplied thereto from a supply line l6'!1, of say 250 volts D. 0., through a series connected current limiting resistor 18, which is shown as an adjustable type but may be of fixed resistance value. The resistor may suitably provide 50 per cent I. R. drop under starting conditions, or such other selected voltage as may be desired. A current relay I9 is connected in the armature circuit of the mill motor 20 and at its switch 80 controls the circuit of relay 8i having a normally open switch 82 in the circuit between resistor 18 and line I4 01' the armature loop circuit. A second control relay 83 having normally open switch 84 connected in the line M is provided. By actuation of a suitable start switch 85, relays BI and 83 are adapted to be energized to close the series supply circuit and the loop circuit so that machine 25 is supplied with armature current for operation as a motor in parallel circuit relation with feed back motor 22. Appropriate electrical energy supply for control is denoted by and polarity signs. The shunt field 86 of machine 25 is connected across supply line '|6'l'l through a field adjusting resistor 81 by adjustment of which the excitation of machine 25 may be regulated for speed and tension control. Control exciter 23 is employed to control the voltage of machine 25 with switch 82 open independently of reel speed, when machine 25 is operating as a drag generator, thereby to compensate for rundown of the strip coil and maintain tension substantially constant, as disclosed and described in copending application of Mathias Michel, Serial No. 41,737 filed July 31, 1948, now Patent No. 2,485,757.

In Fig. 1, upon completion of a rolling operation, the coil on delivery reel will be stripped therefrom in the usual manner. The mill is not decelerated, but continues to run at rolling speed under no load. Since there is no strip in the mill, current drawn by its driving motor 20 has dropped to a low value, and current responsive relay I9 is de-energized. Both relays 8| and 83 are now de-energized and their switches 82 and 84 open. As a result, series motor 22 is deenergized, but its armature is rotating at a speed determined by mill speed, and machine 25 lacks armature current and reel 8 is at rest in readiness to receive a succeeding coil 24 from the charging buggy 2 6.

After loading, the reel is expanded to grip the coil. The outer end of the strip is withdrawn from the coil, passed between the side guides 52 and inserted between the feed rolls 32-33, both having been previously opened. Pulling out a suificient length of strip from the coil to reach the feed rolls is involved in this feed operation and it is facilitated by the provision of conven tional inch circuit including push switch 88 and control resistor 88, adapted to connect the armature of machine 25 directly across the supply line. By depression of switch 88, machine 25 is supplied with reduced armature current, usually a small fraction of its normal current, to cause slow rotation of the coil, the switch 88 being released when the strip reaches the feed rolls.

With the end of the strip between the feed rolls, the side guides and the feed rolls are sequentially actuated, as heretofore described, first to center the strip and then to grip the strip, whereupon motor 5| is energized. Thereby, feed roll 32 is rotated to take up slack in the strip, but the motor power is insuflicient to rotate the load represented by coil 24, reel 8 and its driving mechanism. "Simultaneously with energization of motor 5|, the mill operator may depress start switch to cause flying entry of the strip into the mill. It may be assumed that the mill is being operated at its top speed.

Closure of switch 85, it will be seen, energizes relays 8i and 83 and they close their switches 82 and 84. Relay 83 at its switch closes a point in a self-sealing circuit, subsequently closed at switch 9| of current relay 19, so that after such closing, the start switch may be released and loop relay 83 held in under control of the current relay. At the instant of closing switches 82 and 84, a current flows through the starting resistor 78 and armatures 12 and I3 of motor 22 and machine 25, whereupon the latter operates as a motor since its field 85 is energized. At this time, the voltage drop across motor 25 only equals the I. R. drop across its armature 13 since it is stationary. Series motor 22, however, is running at a speed proportional to mill speed; therefore, a very light current through its series field 92 will create a C. E. M. F. which is approximately equal to the I. R. drop across armature of motor 25. Hence, practically all of the starting current through the starting resistor 18 passes through the armature of motor 25 and in combination with its excitation provides a high starting torque. Hence, the motor 25 starts to accelerate reel -8 and coil 24 to pay off the strip S at a continuosly increasing rate. Simultaneously, motor 5| accelerates at a faster rate and keeps the strip taut between the coil and feed rolls, the strip in effect being pushed by the feed rolls through the horizontal guide tunnel, past the open bridle rollers and into the roll pass between the mill rol-ls. Acceleration of reel 8 and coil 24, by motor 25, augmented by the small torque of motor 5!, is designedly at such rate as to cause the strip to be traveling at approximately mill roll speed by the time the end of the strip reaches the mill rolls and enters between them. Some speed differential between feed rate and mill speed is permissible, as hereinabove pointed out. the difference existing at entry being primarily determined by the rupture strength of the strip. By thus imparting kinetic energy to the coil and reel mass to an extent representing a predetermined percentage of the starting inertia. which otherwise the strip would be required to overcome, the strip is not required to sustain a stress exceeding its tensile strength when it enters the mill even though the mill is running at rolling speed, and consequently the possibility of strip rupture is eliminated.

A given strip mill as designed and installed will have a top strip delivery speed, and while it may be operated at top speed, more frequently and usually it is operated at a lesser rolling speed. For example, a mill designed for 1,200 feet per minute top speed, may often be operated at 1,000 feet per minute rolling speed. In addition, there is a maximum coil size as to diameter and width which the reel serving the mill can safely accommodate. Hence both the top mill and the W. R? of the reel with maximum coil size are fixed factors. In conformity with the invention, a machine 25 is provided such that for top mill speed and largest coil size it will, with a. given armature starting current, accelerate the coil to the strip feed rate correlated or proportioned, as above described, to mill speed, and run at a fixed speed. However, strip entry occurs while the motor is still accelerating.

Under the assumed case that the rolling mill is being operated at its top speed, upon closure of switches 82 and 84 and acceleration of motor 25, the C. E. M. F. of this motor builds up and opposes the line voltage and gradually reduces the starting current. At the same time, an increased current will flow through the series motor 22 and build up its C. E. M. F. at the same rate. This counter-voltage ends up at a value determined by the speed of armature I2 and I. R. drop across starting resistor 18. Since motor 22 is drivingly connected with the mill drive and is running at a, speed proportional to mill speed, its counter-voltage and armature current are proportional to mill speed. At top mill speed, this counter-voltage of motor 22 is maximium and its armature current is minimum and for equilibrium requires a, higher terminal or end voltage in the loop circuit. Reel motor 25 must accelerate until its counter-voltage and I. R. drop balance this voltage in the loop as determined by the end voltage of the series motor. By changing the excitation on motor 25, its starting torque, as well as its end speed may be changed, as desired. Since the accelerating torque is not to be unduly prolonged, it is preferred to employ a strong field on motor 25 for high starting torque. This torque is sufiicient to accelerate the reel and coil as hereinabove described.

It is to be noted and appreciated that if the strip speed at entry is only 80 per cent of mill roll speed and consequently is jerked up to 100 per cent roll speed, the counter-voltage of motor 25 is still lower than the end voltage in the loop. Therefore, motor 25 is still receiving a current in the accelerating direction which continues until supply of armature current is discontinued.

When the mill is operated at a speed lower than its top speed, the strip feed rate needs be made proportionally lower. This is executed automatically by motor 22. Stabilization between its terminal voltage and the opposing countervoltage and I. R. drop will necessarily have to occur with a, lower end voltage because its armature is being rotated at a lower speed. Consequently reel motor 25 will accelerate as before, but since a lower terminal voltage is impressed, its counter-voltage and I. R. drop will come into balance therewith at a lower speed.

Summarizing the operation of the acceleration control in other words, at starting, resistor 18 and I. R. drop of armature of motor 25 primarily determine the starting current and hence the accelerating torque, while the resistor 18 and series motor 22 determine the end voltage in the armature loop circuit at a given mill speed. Thus. if the mill speed is changed, this end voltage impressed on motor 25 is also changed, and the reel motor will accelerate, but only to a speed determined by the new end voltage. as in the case of the mill operating at top speed, the strip is accelerated and at least enters the mill while traveling at such a speed proportioned to mill speed (whether higher or lower) that the strip is effectively relieved of shock loading in excess of its tensile strength. This automatic readjustment of the strip feed rate or the entry speed is very important as it eliminates the necessity for the operator to resynchronize the entry speed of the strip for various mill speeds.

The resistance of series resistor 18 may be reduced and higher voltage applied to the loop circuit to effect faster rate of acceleration, if necessary. Also, when smaller coils of strip are being operated upon, the value of the series resistance may be conformably increased so as to lower the torque and acceleration rate to a point compatible with the lesser load.

Upon entry of the strip between the mill rolls, the operation of machine 25 as a motor is discontinued, manually if desired, but preferably automatically as here disclosed, and it is caused to operate as a drag generator to back tension the strip. As a result of the strip entering the mill, the current of. mill motor 20 increases and relay l9 energizes. At switch 9|, it closes the holding circuit for loop relay 83, so that the operator may release start switch and at its switch 80, it opens the energizing circuit for relay 8|. This relay de-energizes and opens the circuit between the resistor 18 and the armature loop, whereupon armature current is cut off and motor 25 no longer drives the coil, but instead is driven by it. Since the loop circuit is closed at switch 84, voltage generated by the armature of machine 25, now acting as a drag generator, circulates through the loop and energizes series motor 22, to assist in driving the mill. The electrical power thus generated may be otherwise utilized, as desired. In lieu of the current responsive relay to control switch-over from reel drive to reel hold-back, the well known photoelectric cell type of control responsive to movement of the end of the strip past the mill rolls may be used, if desired.

During strip rolling, the value of back tension in the strip will be maintained substantially constant by the operation of the exciter regulator 23, as described in the application hereinabove referred to, the value being preselected by adjustment of the field control rheostat 81, along with concurrent adjustment of shunt field controlling rheostat 93 of exciter 23, for regulation at the new tension value. Other types of tension regulators well known to the art may be substituted, including those employing a tensioning roller adapted to bear upon the strip.

After strip entry into the mill has been effected, the guide device 52 and the feed rolls 3233 may be actuated to open position and the feed motor 5| stopped. However, if desired, the feed rolls may be kept closed and motor 5| caused to operate as a drag generator during rolling of the strip. Rolling proceed in normal fashion. Then when the coil is unwound to but a few remaining turns upon the reel, the bridle rollers are closed upon the strip thereby to impose enough tension on the strip to prevent the trailing end portion from tearing up in the mill. The amount of this back tension imposed upon the trailing end portion of the strip may be increased by again closing the feed rolls if they have been opened and causing motor to operate as a drag generator. Then when the strip has passed through the mill, the coil on the delivery reel is stripped therefrom in readiness for a succeeding rolling operation.

From the foregoing it will be appreciated that because of the manner of effecting strip entry at continuous rolling speed with immediate application of back tension to the strip, the production of usable on-gauge material is increased for each coil. In addition, the strip coming from the mill initially is more flat and free from transverse bow, thus facilitating initiation of its recoiling on the delivery reel at high rolling speed.

In conformity with the requirements of the patent statutes, the invention has been particularly described in detail and the best embodiments for practicing the invention pointed out. However, it is to be understood that the invention may be otherwise practiced than herein specifically described and the apparatus variously constructed and modified without departing from the spirit and scope of the invention as pointed out in the appended claims.

What is claimed is:

1. In apparatus for feeding successive coils of metal strip to a strip rolling mill for cold rolling withouLredinzing.the, rolling speed of the mill, an unwindurgel for a strip' coifdisposed in front of said mill, a dynamo-electric machine connected to said reel, means for energizing said machine as a motor, said machine having capacity as a motor to continuously accelerate said reel and coil from standstill to a strip feed speed greater than said rolling speed by the time the strip unwound from said coil reaches said mill for entry, said energizing mea s including a resistance in series with the armature of said machine to limit the armature current, a series motor continuously driven-from said mill at a speed proportional to said rolling speed and connected electrically across the armature terminals of said machine to control said acceleration and render the strip speed at entry into the mill proportional to said rolling speed, motor driven pinch roll means interposed between said mill and said reel to "receive the strip unwound from said coil preliminary to its accelerated feed into said mill,

and adapted to be accelerated at a higher rate than that of said reel and coil whereby the strip between said coil and said pinch roll means is kept taut, and strip guideameans extending between said pinch...roll means and said mill through which the strip in efiect is pushed by the former for entry into the latter.

2. In apparatus for feeding successive coils of strip metal to the work rolls of a strip rolling mill for cold rolling without reducing the rolling speed of the mill, a series motor having its armature coupled to said mill for rotation at a speed proportional to said rolling speedjexpansible reel means for axially supporting t strip coil and rotating the same for delivery of its strip to said work rolls) a dynamo-electric machine having its armature geared to said reel means and its exciting field connected across a supply source, said machine having capacity as a motor to accelerate said coil and reel means from stand- 12 still to a strip feed speed greater than said rolling speed by the time the unwound strip reaches said rolls for entry, a loop circuit connecting said armatures electrically with each other, circuit means connecting said loop circuit across said supply source including a control switch and a current limiting resistance in series between said source and one side of said loop circuit, manually operated means for eifecting operation of said control switch to close said connecting circuit when strip from a coil loaded on said reel means is to be entered between said work rolls, whereby said machine accelerates said reel means and coil to a strip delivery speed rendered proportional to said rolling speed by the action of said series motor before the strip enters between said work rolls, and means responsimentry of the strip between said work rolls for effecting opera 1011 of said control switch independently of said manually operated means to open said connecting circuit and thereby cause said machine to function as a drag generator energizing said series motor, to back tension the strip during its passage between said rolls.

3. In apparatus for feeding successive coils of strip metal to the work rolls of a strip rolling mill for cold rolling without reducing the rolling speed of the mill, an unwind reel for a strip coil arranged to grip and rotate the coil for delivery of its strip to said rolls, a dynamo-electric machine having its armature geared to said reel and its field winding continuously excited during alternate operation thereof as a motor and a drag generator, said machine having capacity as a motor to accelerate said coil and reel means from standstill to a strip feed speed greater than said rolling speed by the time the unwound strip reaches said rolls for entry, a series motor having its armature coupled to said mill motor, a loop circuit connecting said armatures and containing a control switch for opening and closing the loop, a series circuit connecting said loop circuit to opposite sides of a supply source for 1 supply of armature current to said armatures and including an adjustable current limiting resistor and a second control switch in series disposed betweensaid source and one side of said loop circuit, a starting switch, means connecting said starting switch' with each of said control switches for effecting concurrent closure of said loop and series circuits, whereby said machine accelerates said reel and coil to an extent determined by the speed of said series motor and renders the strip delivery speed at entry proportional to said rolling speed, {control means responsive to entry of the strip between said rolls for automatically operating said second control switch'to open said series circuit,)and interlocking connections under control of sai control nYa'aTrTs'Tnsuring operation of said first named control switch to maintain said loop circuit closed and cause said machine to function as a drag generator until the trailing end of the strip leaves said rolls.

4. In apparatus for feeding successive coils of strip metal to a strip mill for cold rolling without reducing the rolling speed of the mill, a strip coil unwind in front of said mill and having an expansible and rotatable element for axially supporting and gripping a strip coil for unwinding,"

a dynamo electric machine having its armature connected to said rotatable element and its exciting field connected across an electrical supply source and excited at full field strength, means comprising a switch and a current limiting resistor connecting said armature across said supply source to effect operation of said machine as a motor by closure of said switch, said machine having capacity as a motor to accelerate said rotatable element and coil from standstill to a strip feed speed greater than said rolling speed by the time the strip unwound from said coil reaches said mill for entry, and a feed back motor having its armature electrically connected in shunt with the armature of said machine and mechanically coupled to said mill for rotation at a speed proportional to said rolling speed for controlling said acceleration and rendering strip .feed speed at entry proportional to said rolling speed.

5. In apparatus for feeding successive coils of strip metal to a strip mill for cold rolling without reducing the rolling speed of the mill, a strip coil unwind in front of said mill and having an exfiafsilileafid'r'otatable element for axially supporting and gripping a strip coil for unwinding, a dynamo electric machine having its armature connected to said rotatable element and its exciting field connected across an electrical supply source and excited at full field strength, means comprising a switch and a current limiting resistor connecting said armature across said supply source to effect operation of said machine as a motor by closure of said switch, said machine having capacity as a motor to accelerate said rotatable element and coil from standstill to a strip feed speed greater than said rolling speed by the time the strip unwound from said coil reaches said mill for entry, a series motor connected to said mill for rotation of its armature at a speed proportional to said. rolling speed, and having its said armature electrically connected across the armature terminals of said machine for controlling said acceleration and rendering strip speed at entryinto said mill proportional to said rolling speed, and means responsive to entry of the strip into said mill for actuating said switch to open position thereby disconnecting both said armatures from said supply source.

MATHIAS MICHEL.

References Cited in the file ofthis patent UNITED STATES PATENTS Number I Name Date 2,310,098 Lessmann Feb. 2, 1943 2,326,079 Tyrrell Aug. 3, 1943 2,342,790 Cook Feb. 29, 1944 2,484,825 Harris Oct. 18, 1949 2,485,757 Michel Oct. 25,1949 

